1. Technical Field
The present invention relates to a liquid ejecting apparatus that ejects a liquid from nozzles.
2. Related Art
A liquid ejecting apparatus is an apparatus that is provided with a liquid ejecting head, and that ejects various kinds of liquid from the liquid ejecting head. For example, there are image recording apparatuses such as ink jet type printers and ink jet type plotters, but recently, liquid ejecting apparatuses are being applied in various production apparatuses by utilizing the feature that liquid ejecting apparatuses can reliably land an extremely small amount of a liquid on a predetermined position. For example, liquid ejecting apparatuses are applied in display production apparatuses that produce color filters such as liquid crystal displays, electrode formation apparatuses that form electrodes such as organic Electro Luminescence (EL) displays and Field Emission Displays (FED), and biochip production apparatuses that produce biochips (biotips). Further, in recording heads for image recording apparatuses, liquid ink is ejected, and solutions of the respective color materials of R (Red), G (Green) and B (Blue) are ejected by color material ejecting heads for display production apparatuses. In addition, in electrode material ejecting heads for electrode formation apparatuses, a liquid electrode material is ejected, and solutions of living organic matter are ejected by living organic matter ejecting heads for chip production apparatuses.
A liquid ejecting head such as that mentioned above is configured to introduce ink into pressure chambers from a cartridge in which ink (a type of liquid) is accommodated, bring about a pressure fluctuation in ink inside the pressure chambers, and eject ink from nozzles that lead to the pressure chambers. In addition, a maintenance process that is referred to as a flushing operation, which forcibly ejects ink from the nozzles is performed in a liquid ejecting apparatus that is provided with this kind of liquid ejecting head (for example, JP-A-2011-73349). This flushing operation is for example, performed after a cartridge is exchanged, after a predetermined amount of time has passed or the like, in order to expel air bubbles and ink that has thickened. More specifically, the liquid ejecting head is moved to a position that is shifted from a recording region, and ink is repeatedly ejected at this position.
Given that, since a surface of ink (the meniscus) that is exposed inside the nozzles of the liquid ejecting head is exposed to the atmosphere during the execution of a printing process on a recording medium, moisture in the ink gradually evaporates with the passage of time, and the viscosity of ink in the vicinity of the nozzles increases. When the viscosity of ink in the vicinity of the nozzles (in the periphery of the meniscus in particular) increases, there is a defect in that it is not possible to eject air bubbles and ink that has thickened from the nozzles in a stable manner in the flushing operation. This defect will be described using FIG. 8.
FIG. 8 is a peripheral cross-sectional view of a nozzle 97 that describes circumstances in which ink is ejected in a flushing operation. In addition, in FIG. 8, ink in the periphery of the meniscus, which is exposed to external air is thickened ink (ink with a high viscosity) Ih, and ink that is on a pressure chamber 98 side of the thickened ink Ih is normal ink (ink with a lower viscosity than the meniscus side) In. In the flushing operation, firstly, when the pressure chamber 98 is caused to rapidly contract after the meniscus is drawn into the pressure chamber 98 side by causing the pressure chamber 98 to expand, as shown in FIG. 8A, an ink droplet Id is ejected. Further, after the ejection of the ink droplet Id, as shown in FIG. 9, residual vibrations are generated. That is, after the ejection of the ink droplet Id, as shown in FIG. 8B, the meniscus moves to the pressure chamber 98 side again, and subsequently, as shown in FIG. 8C, the meniscus moves to an ejection side again. Additionally, in the coordinate axis of FIG. 9, the horizontal axis shows time t and the vertical axis shows positions of the meniscus so that a direction that leads toward the ejection side from the pressure chamber 98 side is positive. In addition, a time point that is shown as Pb is a time point at which the ink droplet Id is ejected. Furthermore, an interval between a time point Pa and a time point Pc is substantially equivalent to a specific period Tc (a specific vibration period Tc) of ink inside the pressure chamber 98, and a period of the subsequent residual vibrations is also substantially the same as the specific vibration period Tc.
In this instance, between the time point Pc and the time point Pd, that is, when the meniscus moves to the ejection side as shown in FIG. 8C, since the flowability of the thickened ink Ih that remains in the periphery of the meniscus is poor in comparison with ink In that moves from the pressure chamber 98 side, a portion of air gets trapped in the ink, and the trapped air gets left inside the ink as air bubbles B. The air bubbles B that enter the pressure chamber 98 side get into the pressure chamber 98 side due to a buoyant force or the like, and when the air bubbles B remain in a flow channel, the air bubbles B cause ink ejection defects.